1. Field of the Invention
The present invention is generally directed to a method of recycling colored polyamides. In particular, the method of the present invention is useful in recycling post-consumer materials, such as carpets, that contain colored polyamide fibers.
2. Background
As the amount of available landfill space decreases, and the number of articles manufactured from synthetic polymers increases, the need for environmentally responsible methods for disposal of these polymer-containing articles increases. A welcome alternative to landfill disposal is recycling and reuse of the synthetic polymer material in products which may be the same as or entirely different from the original article.
One significant limitation to the utility of recycled synthetic polymer material is the imparted color. Colorants, additives, or dyes are commonly added to virgin polymers for both practical and aesthetic reasons. However, the colorant, additive, or dye may significantly impair the processability of or degrade the polymer during conventional recycling processes. Further, the presence of colorant, additive, or dye may limit the potential downstream uses of the recycled polymeric material, as any color change desired in the downstream use could be limited if not impossible given the original article's color. In some cases, an article otherwise suitable for recycling is rejected completely and deposited in a landfill simply because its color is undesirable or inappropriate for a particular downstream use.
Processes for stripping dyes from or decolorizing various materials are known in the art. For example, U.S. Pat. No. 4,227,881 discloses a process for stripping dyes from textile fabric which includes heating an aqueous solution of an ammonium salt, a sulfite salt and an organic sulfonate to at least 140.degree. F. (60.degree. C.) and adding the dyed fabric to the heated solution while maintaining the temperature of the solution. In addition to the costly heating and temperature maintenance step, this process has the drawback of producing fabrics which after processing exhibit a remaining color depth. U.S. Pat. No. 4,783,193 discloses a process for stripping color from synthetic polymer products by contacting the colored polymer with a chemical system. The described process uses unstable dispersions of alkyl halides and aqueous solutions of bleaching/oxidizing agents to which specified quantities of acids and surfactant/wetting agents are added. Among the drawbacks are the use of potentially hazardous halogens and the special provisions required to prevent escape of vapors which could cause environmental harm. Further, the use of the chemical system may restrict or eliminate the polymeric material's recycleability. In general, processes which utilize harsh stripping agents destroy the usefulness of the colorant, thus generating a chemical waste stream that must be treated or disposed of in an environmentally conscious manner. These methods can also generate unremovable colorant fragments which limit the downstream recycleability and utility of the color-stripped material.
Thus an unmet need exists for a cost-effective and environmentally friendly process for separating polymers from colorants, additives, or dyes, without degrading or otherwise decreasing the polymeric material's potential use.